1. Field of the Invention
The present invention relates to a testing method that can be suitably used for defect test or bit error rate test of a magnetic recording media used in a hard disk drive or the like and for certification tests such as a parametric (electromagnetic conversion characteristics) test.
Priority is claimed on Japanese Patent Application No. 2008-162277, filed Jun. 20, 2008, the content of which is incorporated herein by reference.
2. Description of the Related Art
Magnetic recording devices represented by a hard disk drive are widely used as an external storage device for an information processing apparatus such as a computer, and have also been used as a picture recording apparatus or the like for recording dynamic images in recent years.
A hard disk drive usually includes: a shaft causing a disc shaped (donut shaped) magnetic recording medium having an opening at the center to rotate as a single disc or to rotate as a plurality of stacked discs coaxially (when a plurality of discs are rotated, the discs are synchronously rotated); a motor coupled to the shaft through a bearing and rotates the magnetic recording medium; a magnetic head used for recording on/reproducing from both sides of the magnetic recording medium; a plurality of support arms to which the magnetic head is installed; and a head stack assembly that moves the plurality of support arms synchronously and delivers the magnetic head to any position on the magnetic recording medium. In addition, a magnetic head for magnetic recording/reproducing processes is usually a floating head and moves over a magnetic recording medium at a certain flying height.
In general, in a magnetic recording medium mounted in a hard disk drive, recording regions known as tracks and sectors are formed in the radial direction and in the track extending direction, respectively. Reading/writing of information in a magnetic recording medium is usually conducted on a unit track basis and on a unit sector basis.
In addition, hard disk drives have conventionally used servo information signals when positioning a magnetic head onto targeted tracks and sectors. The servo information signals are attained by making a magnetic head to read the servo information which has been recorded in a magnetic recording medium in advance. Servo information provides positional information of the recording region in a magnetic recording medium, and thus the current position of the recording region where the magnetic head is positioned can be detected by making the magnetic head read the servo information. Servo information is usually written on a magnetic recording medium radially and in a continuous manner in the radial direction.
In general, a magnetic recording medium is produced by the following steps. That is, a magnetic recording medium is formed by first subjecting the surface of a substrate made of an aluminum alloy, a glass substrate or the like to a texturing treatment or the like, followed by the sequential formation thereon of a base layer, a magnetic layer, a protective layer, a lubricating layer, and the like. Then a glide test and a certification test are carried out on the obtained magnetic recording medium in succession.
A glide test is a test to inspect the surface of a magnetic recording medium for the presence of projections and protrusions. That is, if there is a projection or a protrusion on the surface of a magnetic recording medium which is higher than the flying height (that is, the interval between the medium and a magnetic head) when recording on/reproducing from the magnetic recording medium using the magnetic head, the magnetic head will hit the projection and the protrusion, which may damage the magnetic head or may cause defects in the magnetic recording medium. In a glide test, the presence and absence of projections and protrusions with such heights are inspected (for example, refer to Patent Document 1).
A certification test is conducted on the magnetic recording medium that passed the glide test. The certification test is carried out so that, as in the usual recording/reproducing processes of a hard disk drive, following recording of predetermined signals on a magnetic recording medium using a magnetic head, the signals are reproduced and the recording failure of the magnetic recording medium is detected from the obtained reproduced signals, thereby verifying the quality of the magnetic recording medium in terms of the electrical characteristics, the presence and absence of defects, and the like (for example, refer to Patent Document 2). Accordingly, in the certification test, capability of the magnetic head in recording/reproducing predetermined signals is verified in a similar manner to that performed for the recording/reproducing processes of the hard disk drives. For this reason, as in an actual use method in the hard disk drives, it is preferable to write servo information in a magnetic recording medium using an apparatus known as a servo writer and to perform a test for detecting recording failure of the magnetic recording medium before the certification test.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. Hei 10-105908
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2003-257016
However, in order to write the servo information in a magnetic recording medium, it generally takes from about 30 minutes to 2 hours to write in a one disc medium, although it depends on the size of the magnetic recording medium [and/or TPI (Track per Inch)] or [Number of Track per media surface]. Accordingly, writing of the servo information in a magnetic recording medium prior to the certification test may cause a decline in the productivity of magnetic recording medium. Moreover, due to the increasing demands for magnetic recording media in recent years, an testing apparatus for the certification test which is capable of testing numerous magnetic recording media within an even shorter time period has been required.
In the meantime, the recording density of magnetic recording media has been becoming larger and larger in recent years, and it has been required to carry out a certification test on a magnetic recording medium in a hard disk drive with a high degree of accuracy by employing an testing method, which is even closer to the actual method in which the medium is used.